This study examines the correlates of sexual behavior and sexually transmitted diseases, employing three new data sets from China. (1) Population-based sample. With oversampling of cities and coastal areas that have more varied sexual behavior and greater risks for sexually transmitted diseases (STDs), this nationally representative sample provides data on 3,825 adults age 20-64. This sample allows comparisons to other countries, and of major regional, cohort, and other differences in sexual behavior and disease patterns. (2) Clinic sample. This parallel set of interviews of 845 patients from 16 clinics in 5 cities provides larger sample sizes for the analysis of STDs. Besides being analyzed in its own right, when used with comparable observations from the population sample, the clinic sample makes possible a form of case-control analysis to help delve further into risky sexual behaviors and sexually transmitted diseases. (3) Biomarkers. Based on 4,277 urine specimens from the population and clinic samples, these data provide information on current infections for chlamydia, gonorrhea, and trichomonas. With use of the latest lab techniques, these biomarker data provide both an additional check on the validity of the survey data and material for identifying major risk groups in transitional societies. This proposal is for an additional two years of time for the analysis of these data sets, and for producing a public-use data set that includes direct linkages to comparable U.S. data.